Inorganic glass has excellent transparency and excellent properties, e.g., small optical anisotropy, and therefore, are used previously as a transparent material in wide fields. However, there are problems in that the inorganic glass is heavy and susceptible to damage, the productivity is poor, for example. Consequently, in recent years, transparent polymers as alternatives to the inorganic glass have been developed actively. For example, polymethyl methacrylates (PMMA) and polycarbonates (PC), which are transparent polymers and which have excellent transparency and mechanical properties as well as excellent workability and moldability, are used as molding materials in machines, automobiles, optical apparatuses, electric and electronic fields, and the like. However, known polymers do not have sufficient heat resistance. For example, although the glass transition point of the polycarbonate is 150° C., some optical materials in automobiles and in electric and electronic fields are required to have heat resistance up to 150° C. or more. Consequently, research has been actively conducted on highly heat-resistant polyarylates (PAR), polyether sulfones (PES), and the like. However, some have coloring problems due to elongation of conjugated systems since the content of aromatic groups is high, and there are problems in that, for example, birefringence is increased since optical anisotropy is generated during orientation. When only the optical property is taken into consideration, in general, the aliphatic series have small refractive indices and small main polarizability differences and, therefore, are superior to the aromatic series. However, when the aliphatic series are contained, the degree of freedom of main chain and side chain of the polymer is increased, the glass transition point is lowered and, therefore, the resulting polymers are unsatisfactory from the viewpoint of the heat resistance. In recent years, a cycloolefin polymer (COP) having an aliphatic ring structure has been developed actively. Examples of COPs include ZEONEX produced by ZEON Corporation and ARTON produced by JSR Corporation. These have the aliphatic ring structure and, therefore, the birefringence is reduced, and the glass transition points are relatively high 140° C. to 170° C. However, the method for polymerizing COP is a metathesis ring-opening polymerization method and an ethylene group is included in the main chain, so that this method is insufficient to achieve the object of producing a resin exhibiting a further high glass transition point.
The inventors of the present invention noted phosphorous-based polymers which had high heat resistance and excellent optical properties and which had a Spiro ring structure.
It is well known that the phosphate having a spiro ring is useful as a flame retardant of synthetic polymers, and considerable research have been conducted (for example, U.S. Pat. No. 3,090,799, U.S. Pat. No. 4,178,281, and Japanese Unexamined Patent Application Publication No. 60-133049). These documents describe monomers represented by the following General formula (5), for example, and compositions containing the monomers, and disclose that the monomers and the like exert a high effect of improving flame retardancy:
(Here, R4 represents an alkyl group or an aryl group.).
However, in the documents, the monomers and the like are primarily used as only flame retardants, and the documents do not disclose that the monomers and the like are practically used for heat-resistant molded materials and optical purposes. The monomers and compositions having a phosphorous-containing spiro ring structure according to the above-described known technology cannot be produced as high molecular weight substances, and are unsuitable for optical uses because of being colored.